1. Field of Industrial Application
The present invention relates to a magneto-optical recording medium having information signals recorded on both of lands and grooves thereof and to a method and an apparatus for reproducing the information signals from the magneto-optical recording medium.
2. Description of the Related Art
In general, a disc magneto-optical recording medium termed as a magneto-optical disk contains grooves formed concentrically or spirally on the disk itself. The grooves serve to guide a light beam to be applied onto the magneto-optical disk itself. When recording or reproducing information by applying the light beam onto the magneto-optical disk, the tracking control for the light beam is carried out on the light reflected on the grooves.
This type of magneto-optical disk has been conventionally formed to record an information signal not on the grooves but on the lands located between the adjacent grooves. On the other hand, for the purpose of increasing a recording density, in recent days, a new type of magneto-optical disk is proposed wherein the information signal is recorded on both of the grooves and the lands for widening the recording area.
However, this new type of magneto-optical disk formed to record the information signal on both of the lands and the grooves suffers from a drawback that the information signal is leaked from one track to the adjacent one and thereby a crosstalk is likely to take place, because one groove and the adjacent lands thereto are both served as the recording tracks. By keeping the land substantially equal to the groove in width, setting an optical depth d of the groove to a closer value to .lambda./6 and setting a Kerr ellipticity of a magneto-optical effect caused by a magneto-optical recording film contained in the magneto-optical disk to 0 or a closer value thereto, it is possible to reduce the crosstalk and reproduce the signal from the tracks if the interval between the adjacent tracks is narrow.
FIG. 1 shows relation between a crosstalk and a depth of the groove with a track interval as a parameter. In FIG. 1, a laser beam to be applied onto the magneto-optical disk has a wavelength .lambda. of 690 nm and an objective lens for condensing the laser beam onto the magneto-optical recording medium has a numerical aperture NA of 0.55, where the depth of the groove corresponding to a value of .lambda./6 is about 77 nm.
As is understood from FIG. 1, when the optical depth d of the groove is close to a value of .lambda./6, the crosstalk is made minimal. In case that the track interval is made narrower, the crosstalk is likely to be minimal when the groove is made deeper. That is, when the track interval is made narrower for increasing the recording density, it is necessary to deepen the groove for the purpose of reducing the crosstalk.
Next, FIG. 2 shows relation between a Level of a signal reproduced from the track and a groove depth when the track interval is 0.5 .mu.m. As shown in FIG. 2, the reproduction signal level is made smaller as the groove is made deeper, in which the reproduction signal level becomes minimal when the groove is .lambda./4 in depth. Further, the reproduction signal from the track becomes inferior in frequency characteristic as the groove is made deeper. Hence, from a viewpoint of obtaining a higher reproduction signal level, it is preferable to keep the groove shallower.
As shown in FIG. 1, when the track interval is kept narrower, for reducing the crosstalk, it is necessary to deepen the groove. As shown in FIG. 2, however, if the groove is made deeper when the track interval is narrow, the reproduction signal is degraded.
Hence, conventionally, the magneto-optical disk formed to record the information signal on both of the grooves and the lands has been requested to restrict the interval of the track. This type of magneto-optical disk, therefore, has difficulty in greatly improving its recording density.